Method of screening a color picture tube

ABSTRACT

The screen of a color picture tube is provided with an interlaced pattern of filter components individually transmissive of one of the primary colors, green, blue and red. The filters are applied through a photographic printing process which features a water-based organic photosensitive coating material, including as an ingredient a metallic compound referred to as a luster, and having the property that upon being heated to a predetermined firing temperature the organic constituents evaporate, leaving as a residue an inorganic colorant that is predominantly transmissive to one of the three primary colors. The filter components are dimensioned to overlap at their peripheral portions and define, in the areas of overlap, a light attenuator. The non-overlapping portion of each filter receives a deposit of a phosphor which emits light of the wavelength to which the associated filter component is transmissive.

United States Patent [191 Kachel [54] METHOD OF SCREENING A COLOR PICTURE TUBE Irwin Kachel, Skokie, Ill.

[73] Assignee: Zenith Radio Corporation, Chicago,

Ill.

[22] Filed: Aug. 24, 1970 [21] Appl. No.: 66,455

[75] Inventor:

[52] U.S. Cl. ..96/36.l, 96/34, 96/93, 1l7/33.5, 117/124 [5 6] References Cited UNITED STATES PATENTS 3 ,622,322 ll/l9 7l Brill ..96/38.l

[51] Int. Cl ..G03 5/00, G03c 7/00, G030 1/66 [58] Field of Search ..96/36.l, 34, 38.1; 117/124, 33.5; 313/92 B, 92 R 51 May 22,1973

Primary Examiner-Norman G. Torchin Assi mmin lley Attorney-John J., Pederson and Nicholas A. Camasto [57] ABSTRACT The screen of a color picture tube is provided with an interlaced pattern of filter components individually transmissive of one of the primary colors, green, blue and red. The filters are applied through a photographic printing process which features a water-based organic photosensitive coating material, including as an ingredient a metallic compound referred to as a luster, and having the property that upon being heated to a predetermined firing temperature the organic constituents evaporate, leaving as a residue an inorganic colorant that is predominantly transmissive to one of the three primary colors.

The filter components are dimensioned to overlap at their peripheral portions and define, in the areas of overlap, a light attenuator. The non-overlapping portion of each filter receives a deposit of a phosphor which emits light of the wavelength to which the associated filter component is transmissive.

1 Claim, 5 Drawing Figures METHOD OF SCREENING A COLOR PICTURE TUBE CROSS REFERENCES TO RELATED APPLICATIONS The invention is a further development of the screening process described and claimed in application Ser. No. 830,288, filed June 4, 1969, in the name of Howard G. Lange now U.S. Pat. No. 3,569,761. Related but different processes are described and claimed in application Ser. No. 66,457, of Ronald C. Robinder and application Ser. No. 66,454 of Ghulam A. Khan, both of which are filed concurrently herewith.

BACKGROUND OF THE INVENTION The present invention isdirected to the screening of color picture tubes and is of general application.

Customarily, the screen of a color picture tube has deposits of different phosphor materials which, in response to excitation by the impacting electrons of a scanning beam, emit light of wavelengths corresponding to the primary colors green, blue and red. These phosphors are distributed over the screen in an interlaced recurring pattern and may have any of a variety of configurations but usually are in the form of dots or stripes. The process of this invention is useful irrespective of the specifics of the phosphor deposits but, for convenience, particular attention will be addressed to processing a picture tube screen which is composed of dot triads, each consisting of a dot of green, a dot of blue and a dot of red phosphor material. The triads are distributed over a field constituting the image reproducing areaand it too may have different configurations such as round or rectangular. The rectangular field is the more popular and will be assumed for the screens discussed herein.

As described in U.S. Pat. 3,1 14,065, issued Dec. 10, 1963 to S. H. Kaplan, distinct advantages may be realized through the association of filter components with the phosphor deposits of a color tube. Structurally, by way of illustration, a filter element may be interposed between each phosphor deposit and the faceplate of the tube with the filter element highly transmissive to the wavelength of light emitted by the phosphor when excited but otherwise serving substantially as a light attenuator.

This same general concept is extended in the teaching of the aforeidentified Lange application to achieve what has become known as a black-surround screen of a color tube. Such a screen is described and claimed in U.S. Pat. 3,146,368, issued on Aug. 24, 1964 in the name of Fiore et al. and assigned to the assignee of the present invention. The black-surround screen structure differs from conventional tri-color picture tube screens in two important aspects. The phosphor dots are small so as to be separated from one another by portions of the screen, whereas in conventional tube structures the phosphor dots are essentially in tangential contact with one another. The other and more pronounced difference is that the black-surround screen structure has light-absorbing material in the screen spaces which separate the phosphor deposits. Obviously, for the dot triad screen each phosphor dot is circumscribed or surrounded by light-absorbing material, such as graphite. Such a screen has distinct advantages in respect of both brightness and contrast.

The Lange application further develops the phosphorfilter concept of the Kaplan patent in arriving at still a new screen structure of the black-surround variety but having distinct benefits in simplication of the screening process. It facilitates screening to achieve light-emitting areas or phosphor dots of smaller diameter than the apertures of the color-selection electrode or shadow mask associated with the screen and through which color selection is accomplished in wellknown manner. In the Lange application a first set of filter elements, such as those transmissive of green, are applied to the screen by photographic printing through the shadow mask of the tube, again utilizing printing techniques that are well known. The individual filters are precisely positioned over the screen area and dimensioned by the apertures of the shadow mask and if the photoprinting is accomplished with the mask as it is to be utilized in the finished tube, the filter elements are larger in diameter than is desired of the light-emitting areas which accommodate the phosphor dot deposits. In particular, each filter element has such diameter that it covers not only the elemental screen area assigned to the color that the filter favors but also extends to the periphery of the neighboring screen areas devoted to others of the primary colors.

Where three sets of such filters are developed, of the same size and interlaced over the image area, they overlap in their edge portions. More particularly, they overlap in those parts of the screen area that otherwise separate the multiplicity of light-emitting areas that are to receive phosphor deposits. Where two such filter elements overlap, there is very little transmission to visible light and, accordingly, the overlap portions of the filters contribute the function of black-surround de scribed in the aforeidentified Fiore patent. With the filters in position, the phosphors are applied over them, green phosphor over the green filter elements, blue phosphor over the blue filter elements and red phosphor over the red filter elements. An especially attractive benefit of the Lange teaching is in the simplifica tion of the screening process. The teaching enables the black-surround screen to be formed without any necessity for changing the size of the apertures in the shadow mask before or after screening has taken place. The present invention has the same advantage and is yet a further development of the general process disclosed in the Lange application.

Accordingly, it is an object of the invention to provide a novel process for screening the faceplate of a color picture tube.

It is a particular object of the invention to provide an improved process for screening a shadow mask type of color picture tube having phosphor deposits over lightemitting areas that are smaller in size than the apertures of the shadow mask, such as is characteristic of a black-surround or a post-deflection-acceleration color tube.

It is a most particular object of the invention to simplify processing of a black-surround screen for a color picture tube.

SUMMARY OF THE INVENTION The method of the invention for screening the faceplate of a color picture tube comprises the following steps. The inner surface of the faceplate is coated with a water-based organic photosensitivematerial, including as an ingredient a metallic compound, and having the property that upon being heated to a predetermined firing temperature the organic constituents evaporate to develop as a residue an inorganic colorant that is predominantly transmissive of one of a plurality of primary colors. The metallic component of the coating material may, for the convenience of nomenclature,

, be referred to as a metallic luster about which more will be said presently. In the next step selected portions of the coating are exposed to actinic energy to establish in the coating a latent image of a distribution pattern desired for the colorant over the image area and that image is developed by rinsing the faceplate with water. The faceplate is heated, preferably after all lusters and all phosphor materials have been screened on, to the firing temperature to deposit the colorant over the image area in accordance with the desired distribution pattern.

In one aspect of the invention an aqueous metallic luster is mixed with sensitized polyvinyl alcohol (pva) to prepare a water-based coating material for application to the inner surface of the faceplate being screened. In another aspect, a water insoluble luster is processed in accordance with the Khan application in preparing a water-based photosensitive coating material to which polyvinyl pyrrolidone is added for improved adherence.

BRIEF DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIG. 1 depicts a prior art screen structure which may be fabricated by the processes of the present invention with the shadow mask eliminated for clarity;

FIG. 2 is a cross section of the structure of FIG. 1, taken along line 2-2, with the shadow mask included;

While FIGS. 3-5 are fragmentary views of a screen structure used in describing embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Color tubes as a rule have two principal envelope sections initially separated from one another which facilitates screening. One of these sections is referred to as the cap or faceplate which is constituted by the screen or image area and a circumscribing flange. The other section is conical and is configured as well as dimensioned at its large end to match the flange of the faceplate so that the sections may ultimately be united through frit sealing or any other integrating process. The smaller end of the conical section terminates in a neck which houses an assembly or cluster of three electron guns. The tube structure, apart from its screen and the method of making that screen, may be entirely conventional and need not be considered further.

FIGS. 1 and 2 show a fragment of the screen structure of the above-identified Lange application. It has a substrate that is substantially transmissive of all light wavelengths in the visible spectrum and is the image area or faceplate of the tube. It may be 100 percent transmissive to visible light or may have some filtering attributes further to enhance contrast by having a transmissivity for visible light of perhaps percent or less. There is nothing unique in the structure of the faceplate since the industry is well versed in the art of preparing faceplates with any desired percent transmissivity.

The screen has a plurality of sets of image elements disposed in an interleaved pattern over substrate 10 and characterized by the fact that the elements of each set are excitable to emit light of an assigned one of the colors green, blue and red. The individual image elements are confined within the solid line circle constructions and the legends G, B and R represent their color designations. Collectively, they define dot triads over the screen one of which is designated 1 lg, 1 lb and 1 1r. Element 11g has a cusp-shaped centrally located lightemitting area enclosed by cross-hatching, the significance of which will be described presently. The cuspshaped area is a light-emitting area of the screen and defines the limits of an effective phosphor deposit of this particular image element. It approximates a dot in configuration where the tube, as assumed, has a triad dot screen and an associated shadow mask with circular holes. If the sets of image elements are printed photographically by exposing appropriate coatings applied to the image area with actinic energy directed through the apertures of the shadow mask, the image elements are positioned and dimensioned relative to one another to establish the desired interlaced distribution patterns. It is to be noted that the light-emitting or effective phosphor area of the representative image element 1 lg is smaller in dimension than the hole 12a of the shadow mask 12, a portion of which is shown in FIG. 2 and through which the exposure takes place. In order to avoid unnecessary confusion to FIG. 1, the mask representation has been omitted from that view. When the shadow mask is properly installed in operative position in relation to substrate 10, mask holes 12a are in alignment with an assigned triad of the screen. The registration of the mask holes with the triads is well understood in the art and makes possible color selection by reason of the fact that electron beams passing through such holes selectively impact only an assigned one of the three sets of image elements.

One desirable characteristic of the image elements. typifying the preferred form of black-surround screen has already been mentioned, namely, the effective area of the elemental phosphor deposit is smaller than the area of the holes in the mask. The expression effective area of the elemental phosphor deposit is used to mean that portion of the phosphor deposit that overlies a light-emitting area of the screen and contributes to image reproduction. If any portion of the phosphor deposit overlies a visible light attenuator, it is ineffective in image synthesizing and may be ignored. Another characteristic of the black-surround screen is an attenuator for visible light wavelengths disposed on the portions of the substrate that surround the effective elemental phosphor deposits and such an attenuator is indicated by the crosshatching in FIG. 1 surrounding element 11g. While crosshatching has been utilized with respect to this single element simply for purpose of emphasis, it will be understood that all image elements of the screen are provided with a similar visible light attenuator. The attenuator comprises overlapping filters which individually have a relatively high transmission efficiency for light of only an assigned one of the green,

blue and red colors and a relatively low transmission efficiency for light in the remainder of the visible spectrum. Ideally, the filter components which are overlapped to form the attenuator could be confined simply to the portions of the substrate shown in crosshatching in FIG. 1 but processing simplicity with a performance gain is achieved by utilizing filter components which totally cover an image element and extend over the portion of the substrate separating that image element from its neighbors to constitute in this fashion one component of the overlapping filter of the attenuator. This is mostly clearly represented in FIG. 2 where the filter component of the green image element 11g is designated 13g. It is applied directly over substrate and the green phosphor G is, in turn, coated over its associated filter component 13g. Clearly, the diameter of filter component 13g exceeds the maximum dimension of the effective phosphor deposit G. The filter component therefore extends beyond the area of the image element 1 1g. In like fashion there is shown in FIG. 2 a blue filter component 13b assumed to have been applied to substrate 10 after the application of the green filter component 13g. Similarly, the red filter component 13r has a peripheral portion l3r that extends over the contiguous portion of the green filter 13g. Assuming the red filter to have been the last of the threeto be applied, it will have another peripheral portion l3r" which overlaps a portion 13b of the blue filter component. These overlapping peripheral portions of the filter components are designated by the crosshatching in FIG. 1. If .the filter components are properly related colorimetrically, any portion of substrate 10 where two or more such filters overlap is essentially black, that is to say, has an exceedingly low transmission efficiency in the neighborhood of 10-20 percent or less for. all wavelengths in the visible spectrum.

The discussion of FIG. 2 pointed out that the interlaced filter patterns developed cusp-shaped lightemitting areas, such as that designated 11g. Each such area has a color filter appropriate to the color phosphor to be deposited in the particular area. For example, the phosphor deposit G of FIG. 2 is shown as confined to the light-emitting or elemental picture area of the face plate that is covered solely by filter 13g and is excluded from the light attenuator'comprised of the overlapping filter elements that encircle light-emitting area 11g. This is an idealized condition and a simplification of the drawing. As a matter of practice, if the phosphor G is applied by the same photo printing technique employed in developing'the filter components, the phosphor dot will be essentially the same in diameter as the filter. However, phosphor superposed over the peripheral portions of the filters which overlap to serve as a light attenuator makes no significant contribution to image reproduction and, accordingly, has not been shown in the drawing.

The Lange application, in disclosing a process for fabricating the screen of FIG. 1, makes specific reference to the utilization of vitreous color filter materials deposited in the manner described in US. Pat. 2,959,483, issued Nov. 8, 1960, in the name of S. H. Kaplan. Such filter materials have low fusion temperatures and usually are of the lead borosilicate type to which inorganic colorants are added to establish the desired color filter characteristics. The process of the present invention achieves the desired structure with distinctly different types of materials, specifically, me-

tallic lusters, in contradistinction to the specific process embodiments of the Robinder application, arranged in water-based systems.

A metallic luster, for the purpose of describing this invention, is a metal resinate which is the reaction product of a metal compound or oxide as a base neutralized with, for example, an organic resinic acid. For convenience of expression, such lusters are identified in the appended claims as an organic metallic component and they have the property that upon being heated to a predetermined firing temperature the organic ingredient volatilizes and develops, as a residue, an inorganic colorant. In laymans language, the luster may be described as an inorganic oxide colorant in a vehicle of organic character that disappears on firing. When a film of such a compound is applied to a glass or ceramic substrate and heated to the firing temperature, the deposited colorant imparts an iridescent appearance to the substrate. The color, as a general proposition, may be selected by choice of the metallic ingredient or oxide. By way of illustration, gold with no oxide additive but otherwise constituting the metallic ingredient of a luster develops a reddish colorant. A chrome oxide additive results in a greenish tint, whereas a cobalt oxide additive yields a bluish tint. Green hues may also be attained by combining cobalt nitrate and zinc nitrate. The saturation or depth of color resulting from the use of a given luster is subject to control by dilution, accomplished through the addition of a solvent for the organic metallic component by varying the coating conditions, especially the weight or thickness of thefilm, or both. Experience to date indicates that a desired saturation may be determined empirically to the end that the colorant serving as the filter underlying any particular one of the three phosphor materials of the. screen exhibits filter characteristics optimally associated with the wavelength of emission occasioned by electron excitation of the overlying phosphor.

Metallic lusters are commercially available and are marketed by Hanovia Liquid Gold Division of Engelhard Industries of East Newark, N. J. Very frequently, the formulation of a commercially available luster is proprietary and lusters are obtained under the identifying type numbers. They also generally have an organic ter. The concurrently filed Robinder application addresses itself broadly to the use of lusters in screening color cathode-ray tubes, especially those of the blacksurround variety. The specific process embodiments disclosed in that application feature both the use of water-insoluble lusters mixed with a photosensitive material that is soluble in the solvent of the luster and the use of such a luster applied to the tubefaceplate as one coating layer with which is associated another coating layer, such as pva, that is insoluble in the solvent'of the luster. While both approaches are feasible and have been utilized in preparing color tube screens, it is advantageous to arrange a water-based system for screening with lusters because commercial screening processes and apparatus in current use in the commercial manufacture of color tubes feature water-based systems. Also these water based systems require only a single material application to and processing of the screen as against two materials and two processing sequences as described in the illustrative embodiments of the R0- binder application. These advantages can be realized vehicle and are immiscible with or non-soluble in wawith the present invention which lends itself to at least two different process embodiments. In the first, an aqueous luster comprising a metallic-salt is mixed with a water-soluble photosensitive resist, while in the other a commercially prepared luster, insoluble in water, is processed to prepare a water-soluble photosensitive coating material.

The first embodiment of the invention is predicated on the concept that certain metallic salts, soluble in water, may be used as an aqueous luster that is compatible with a water-soluble polymeric compound and, therefore, adaptable to a luster-bearing photosensitive resist for forming color filters over selected elemental areas of the image screen or faceplate of a color picture tube. More specifically, aqueous chlorauric acid or gold chloride, neutralized to have a pH of about 6, combines with pva and the admixture can be sensitized with a diazo sensitizer or ammonium dichromate. This composition may be applied by brushing or spraying to the inner surface of the faceplate as the first screening step in developing filter elements on the faceplate. The wavelength response of the filter is, as stated above, determined by the metallic ingredient of the coating material and is selected to meet the requirements of the screen. Illustrative formulations for red, green and blue filter components that have been screened in accordance with this embodiment of the invention are as follows:

For red filter elements, 15 grains of gold chloride or auric acid are dissolved in 15000 of deionized water to which ammonia is added to a pH 6. To this is added 100cc of a water-based slurry containing pva in a concentration of 10 percent by weight. To sensitize the pva there is added ml. of a solution of 3 grams of diazo in 100 cc of water.

For green filter elements cobalt nitrate and zinc nitrate in ratio of 1:10 are used as the metallic ingredient. For example, 0.17 gr. of cobalt nitrate, mixed with 1.7 gr. of zinc nitrate is dissolved in 20 cc of water, neutralized, and added to a photosensitized aqueous slurry of pva in a concentration of 4 percent by weight.

For the blue filter elements 15 gr. of gold chloride mixed with 5.8 gr. of bismuth nitrate is dissolved in 50 cc of water and the solution is neutralized with ammonia. This is added to an aqueous slurry of pva having a concentration of percent by weight and sensitized with a diazo sensitizer or ammonium dichromate.

When commercially available lusters are to be employed, as distinguished from the aqueous lusters of the foregoing formulations, a different process of slurry preparation is necessary because commercial lusters are insoluble in water and yet the objective is to include the luster as an ingredient of a water-based photosensitive slurry system. Broadly speaking, the desired result is accomplished by preparing, as the coating material, an emulsion with water in continuous phase having dispersed therethrough oil as a liquid vehicle for a precipitate of a chosen metallic resinate. Such an emulsion may be prepared by using a polymeric compound that is compatible with both the solvent of the luster and with water. However, commercial lusters may be emulsified directly, as described and claimed in concurrently filed application Ser. No. 66,454 of Ghulam A. Kahn.

In practicing this invention a luster, chosen for the desired color,is heated to boil off its solvent. For example, 35 cc of any type luster solution is heated to about 150 C for an interval of 5 to 10 minutes. This temperature is very much less than the firing temperature of the luster, which may be about 450C, and evaporates the solvent leaving a thick or viscous liquid containing metallic resinates, and remnants of the solvent and resins such as oil of lavendar and gum damar of the original luster solution. To this thick liquid, and while it remains hot, is added a quantity (4 grs.) of a polymeric compound, such as polyvinyl pyrrolidone (pvp), which is soluble in water and has a liquifying temperature such that it dissolves in the hot thick liquid. This mixture is cooled and is then dissolved in cc of methyl alcohol which, in turn, is soluble in water. Thereafter, 200cc of water is added and then 200cc of 5 percent pva. Finally, the coating material is sensitized by mixing in 7cc of 10 percent ammonium dichromate. This completes the preparation of the coating material which is an emulsion having water in continuous phase and a dispersion of oil bearing the metallic resinate.

The direct emulsification process of the Khan application may be improved with pvp as an additive. For example, to 50 ml of Hanovia green luster A-2173 is added 6 ml of an emulsifying agent such as Alipol CO 436 of GAF Corporation, New York, N.Y.. This is thoroughly mixed ultrasonically for about 5 minutes and then ml of water is added as increments over 3 minutes as the mixing is continued. To this emulsion is added 7 ml of 10 percent pvp and mixed. A solution is then prepared of 62 ml 10 percent pva, 230 ml water and 15 ml 10 percent ammonium dichromate and mixed with the luster-pvp emulsion.

Other lusters that have been prepared in accordance with the foregoing processes are distributed by Hanovia under the following type designations: A-2000 (red) and A-2177 (blue).

Having prepared the coating material by means of any of the aforedescribed processes, the next step in screening is to cover the inner surface or image area of the faceplate of the tube with a layer of the coating material which includes as components a metallic luster and an organic photosensitive resist. The specifics of the luster chosen are, of course, determined by the color of the filter elements to be developed. For example, it may be assumed that green filters are to be laid down first in which case the green luster is selected. The pva resist is of the negative type and loses its solubility in water when exposed to actinic energy, such as ultraviolet radiation.

After covering the screen with a layer 20 of a coating material, it is dried in an oven or by infrared lamps although the drying temperature must be kept well below the firing temperature of the luster. When layer 20 is dried, preselected portions of it are exposed to actinic energy to establish in the coating a latent image of a distribution pattern desired for the colorant being processed. This step is very similar to known photoprinting techniques employed in screening color tubes. It entails exposing the coated substrate 10 with ultraviolet light directed through the shadow mask 12 (not shown in FIG. 3) in its proper position relative to substrate 10 and with the light source positioned to simulate the electron beam of the tube in process assigned to excite the green color phosphor. As a result of the exposure, portions 20g of the pva layer are rendered insoluble in water and constitute a latent image of the distribution pattern desired for the green colorant. The next process step comprises developing that image which simply requires rinsing or washing the screen with water to remove the unexposed pva, giving the screen arrangement of FIG. 4 where the latent image is developed in the pva in the form of insolubilized dots 20g disposed as desired over the image area. The screen is then dried.

In preparing black-surround screens, the apertures of mask 12 used in the exposure step have the same diameter as the mask as is finally installed in the tube. Therefore, the distribution pattern for the green colorant is essentially the same as that indicated by the circles of FIG. 1 having the legend G although at this juncture the colorant will not have been deposited. To complete the process, confined simply to establishing the green filter elements in a desired pattern of distribution over the image area, the final step is heating the faceplate to the firing temperature which is that temperature at which the organic ingredient of the metallic luster volatilizes and deposits the colorant on the substrate.

Sets of red and blue filter elements, interlaced with themselves and with the green filter elements, are established by repeating the coating, exposure and development steps discussed in relation to the development of the green filter elements. Two changes are necessary in each of these additional two cycles. In the first place, a metallic luster is to be chosen that is appropriate to the phosphor assigned to the elemental areas of the faceplate on which the filter element is to be provided. That is to say, the filter elements deposited in the areas denoted by the circles having the legend R are to be predominantly transmissive to the wavelength of light emitted by the red phosphor and the elements deposited in the circular areas having the legend B are to be predominantly transmissive to the wavelength of light emitted by the blue phosphor. The other change has to do with the location of the light source in the exposure step. In creating the red filter elements, the light source is positioned to simulate the gun of the tube in process which is assigned to excite the red phosphor, while the exposure in processing the blue filter elements is from a light source simulating the electron gun assigned to blue.

Each exposure takes place through the same shadow mask which assures the desired interlaced patterns with the filter elements precisely located in position and precisely controlled as to dimension. Like the structure previously described in connection with FIG. 1, the filter elements have overlapping portions and where they overlap they define an attenuator for visible light. Accordingly, the filter structure resulting from three cycles of the processing steps described above is essentially the same as that explained in connection with the structure of FIG. I. There is an election of heating the faceplate to the firing temperature as the final step of each cycle of the process for developing one set of color filters or, as an alternative, a single heating step may be employed to deposit the colorants of each of the three sets of filter elements at the same time.

The discussion thus far has concerned only the formation of filter elements on the screen or substrate but obviously it is necessary to apply phosphors to complete the screen structure.

Returning to a consideration of the process explained with the aid of FIGS. 34, it will be recalled that the process steps developed the green filter elements. Having established these elements of the appropriate size and distribution over the image area, the screen may now be coated with a water soluble slurry having green phosphor in suspension. That slurry, of course, is photosensitive and generally is dichromated pva. It is exposed through the shadow mask and with an ultraviolet lamp positioned to simulate the green electron gun to solubilize those portions of the green phosphor bearing slurry that are superposed over the previously formed green filter elements. Washing the screen with water develops the green phosphor deposits, giving the screen structure of FIG. 5 wherein the green filter elements are designated 20g and the green phosphor deposits are designated 22g. If the substrate had previously been fired to deposit the colorant represented at 20g, the phosphor particles may be deposited over the filter elements in bakeout of the screen. If desired, a single bakeout step may be utilized to deposit the colorant 20g and also to deposit the green phosphor, driving off the organic volatilizable components of both the metallic luster and the photosensitive slurry.

Of course, three phosphor materials must be applied. The blue and the red may be laid down over their associated color filter elements in the manner described in developing the green phosphor deposit 22g. The same type of changes are necessitated, however, as pointed out in developing the red and blue color filter elements. Specifically, the phosphor ingredient of the slurry and the position of the exposing light source must be properly related to the color in process but this is well known in the art and need not be further discussed. The order in which the three colors are applied, both in respect of the filter element and the phosphors, is of no great significance although usually they are processed in the sequence green, blue and red. As a practical matter, the three sets of color filter elements and the three sets of phosphor deposits will be completed before any heating step takes place. And, if desired, the three sets of color filters may be photo-printed first followed by the application of the three phosphor materials. It is found that the bakeout step conventionally undertaken in screening raises the faceplate to 450 C. which is an acceptable firing temperature for metallic lusters. It achieves deposition of the various colorants and also drives off the organic ingredients of both the metallic luster deposits and the insolubilized phosphor bearing slurry deposits.

The described process has been found effective in screening black-surround color picture tubes with a minimum of process steps. The metallic lusters are compatible both with the remaining processing steps of the color tube and its operation and lusters of acceptable filter characteristics, in relation to the various phosphor materials of the screen, are commercially available for use.

Particular improvement in screening with photoluster emulsions has been realized by the addition of a water-soluble polymeric binder, such as pvp. A representative formulation has been given above. It has been found that the additive provides greatly improved adherence of the luster to the glass faceplate as well as improved repeatability of the screening application. Moreover, the screening emulsion with this additive has a milky or off-white appearance and is of a much lighter color than exits without the additive. The whitening effect of pvp results in a marked reduction in exposure time, reducing it to approximately one half.

The invention is not restricted to the preparation of color tube screens having effective phosphor deposits that are smaller than the openings of the colorselection electrode or shadow mask, as is the case with black-surround and post deflection focus tubes. The inventive process may be used to advantage in applying a filter, appropriately matched colorimetrically, to the phosphor receiving elemental areas of an otherwise conventional color tube.

While particular embodiments of the invention have been shown and described, itwill be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. The method of screening the faceplate of a color tube which comprises:

coating the inner surface of said faceplate with a water-based coating material comprising; sensitized polyvinyl alcohol in which is dispersed an emulsion of a water insoluble organic metallic luster and polyvinyl pyrrolidone, said metallic luster having the property that upon being heated to a predetermined firing temperature the organic constituent thereof volatilizes producing a residue of inorganic colorant that is substantially transmissive to light of one primary color;

exposing preselected portions of said coating to actinic radiation to develop in said coating a latent image of a distribution pattern desired for said colorant;

developing said image by rinsing said faceplate with water to remove non-pattern areas of said coating;

and heating said faceplate to said predetermined firing temperature to volatize said organic constituent. 

